The major thrust of our proposal will be the isolation and characterization of enzymes involved in nucleic acid metabolism. We are concentrating our efforts on enzymatic reactions involved in the replication of DNA with particular emphasis on the replication of the replicative form of phiX174 DNA to yeild more replicative forms and single-stranded phiX174 DNA. These two reactions involve many of the proteins essential for E. coli DNA replication as well as viral coded proteins. The enzymes which are essential for E. coli DNA replication will be further characterized and highly purified. A number of these reactions involve the alteration of the structure of DNA; the role of superhelicity in DNA replication will also be examined. A number of the reactions observed with E. coli proteins are now being extended to eukaryotic systems.